Hold-back valve for single release air brakes

Abstract

A hold-back valve for single release air brakes includes a plug valve member in a chamber of a valve body and rotatable between at least two positions to establish paths of different resistance to flow between air inlet and outlet passages in the valve body. The plug has spherical central portion with a flattened surface and the spherical central portion is sealingly engageable with one end of a hollow cylindrical flexible packing surrounding the opening of the air inlet passage to the chamber in the valve body. The rotatable plug has passages therethrough to define two or three different flow paths when particular passages of the plug are connected between the air inlet and outlet of the valve body.

What is claimed is: 
     
       1. A hold-back valve for single release air brakes comprising a valve body having a chamber therein and air inlet and air outlet passages opening to said chamber, a plug valve member having passage means therethrough disposed in said chamber and rotatable between at least two positions to define paths of different resistance to flow between said air inlet and outlet, said plug having a central portion shaped as a sphere having a flattened surface, and a hollow cylindrical flexible packing around the opening of said air inlet passage to said chamber, said packing having one end facing toward said plug central portion and said one end shaped to conform to the spherical surface thereof, said plug valve member comprising first and second cylindrical extensions on said central portion, said first extension having a larger diameter than said second extension and the diameter of said second extension being smaller than that of said central portion, and means on the end of said first extension for defining an external flange thereon. 
     
     
       2. A hold-back valve as claimed in claim 1 wherein said chamber has a diameter defining a bearing surface for said first extension, said chamber having first and second openings to the exterior of said valve body, said first opening receiving said first extension external flange means and said second opening defining a bearing surface for said second extension. 
     
     
       3. A hold-back valve as claimed in claim 2 wherein said second extension projects outwardly of said valve body, a handle having an annular member fastened to said second extension projection, said annular member and said external flange means limiting axial movement of said plug with respect to said valve body. 
     
     
       4. A hold-back valve as claimed in claim 3 and further comprising a spring-loaded pin in a bore in said valve body engageable with recesses in a groove in said handle annular member to lock said handle in position. 
     
     
       5. A hold-back valve as claimed in claim 4 wherein said plug valve member is rotatable between three positions and said passage means define a direct exhaust path, a slow exhaust path and a high-pressure hold-back path, said recesses so spaced that said plug is pivotable between two end positions defining slow exhaust and direct exhaust paths respectively, there being a further recess to lock said plug in a central position. 
     
     
       6. A hold-back valve as claimed in claim 1 wherein said one end of said cylindrical packing and said spherical central portion of said plug are engageable such that said plug is centered within said valve body. 
     
     
       7. A hold-back valve as claimed in claim 1 wherein said air inlet and outlet define an angle of substantially 90° with each other, said plug member passage means comprises a first through-bore for the non-throttled passage of air therethrough and a second bore at substantially 90° from said first bore extending from the interior of said first bore for the throttled passage of air therethrough. 
     
     
       8. A hold-back valve as claimed in claim 1 and a diaphragm positioned over the end of said air outlet passage opening to the exterior of said valve body. 
     
     
       9. A hold-back valve as claimed in claim 8 and a holding element attached to the central portion of said diaphragm and mounted in a bore in said valve body. 
     
     
       10. A hold-back valve as claimed in claim 8 wherein said exterior air outlet opening is outwardly inclined and the edge of said diaphragm engages said inclined opening. 
     
     
       11. A hold-back valve as claimed in claim 1 wherein said plug valve member is rotatable between three positions and said passage means define a direct exhaust path, a slow exhaust path and a high-pressure hold-back path. 
     
     
       12. A hold-back valve as claimed in claim 11 and a spring-loaded check valve within said plug passage means. 
     
     
       13. A hold-back valve as claimed in claim 12 wherein said spring-loaded check valve comprises an adjustable spring such that the hold-back pressure can be selectively adjusted. 
     
     
       14. A hold-back valve as claimed in claim 12 wherein said passage means comprises a large diameter third bore extending perpendicularly to said plug flattened surface and having a third opening on said flattened surface, said check valve being disposed within said third bore. 
     
     
       15. A hold-back valve as claimed in claim 14 and a flat annular member retained in said third bore by a lock ring and a spring being supported against said flat annular member. 
     
     
       16. A hold-back valve as claimed in claim 15 wherein there is a fourth opening in said plug between said third bore and the surface of said plug opposite from said flattened surface, a valve seat in said third bore surrounding said fourth opening, said check valve having a flat valve member with a flexible packing on one side thereof engageable with said valve seat under the action of said spring. 
     
     
       17. A hold-back valve as claimed in claim 16 and means projecting on the other side of said flat valve member for centering said spring. 
     
     
       18. A hold-back valve as claimed in claim 16 wherein said flat valve member is substntially square. 
     
     
       19. A hold-back valve as claimed in claim 16 wherein said plug member passage means further has fifth and sixth openings to the surface of the plug member. 
     
     
       20. A hold-back valve as claimed in claim 19 wherein said fourth opening, said check valve and said third opening define a high hold-back pressure path. 
     
     
       21. A hold-back valve as claimed in claim 19 wherein said fifth opening and said third opening define a direct exhaust path. 
     
     
       22. A hold-back valve as claimed in claim 19 wherein said sixth opening and said fifth opening define a slow exhaust path. 
     
     
       23. A hold-back valve as claimed in claim 19 wherein the axis of said fifth opening defines an angle of about 65° with the axis of said fourth opening. 
     
     
       24. A hold-back valve as claimed in claim 19 wherein the axis of said sixth opening defines an angle of about 80° with the axis of said fourth opening. 
     
     
       25. A hold-back valve as claimed in claim 19 wherein the axes of said third, fourth, fifth and sixth openings intersect at the geometrical center of said spherical central portion of the plug. 
     
     
       26. A hold-back valve as claimed in claim 19 wherein the diameters of said fifth and third openings are substantially large with respect to the diameters of said fourth and sixth openings. 
     
     
       27. A hold-back valve as claimed in claim 19 wherein the diameters of said fourth and sixth openings are substantially equal. 
     
     
       28. A hold-back valve as claimed in claim 16 wherein said third and fourth openings are aligned along a common axis. 
     
     
       29. A hold-back valve as claimed in claim 11 wherein said plug is turned through an angle of 45° from said slow exhaust path to said high-pressure hold-back path and is turned through an angle of 90° from said high-pressure hold-back path to said direct exhaust path. 
     
     
       30. A hold-back valve as claimed in claim 1 and a ring of rigid material enclosing the peripheral portion of said one end of said cylindrical packing.